The present invention generally relates to wireless Internet Protocol (IP) networks. More specifically, this invention relates to the soft handoff of mobile terminals in wireless Code Division Multiple Access (CDMA) IP networks.
Modem wireless networks commonly employ CDMA techniques to communicate information between a mobile terminal and a base station. Modulating information using CDMA techniques provides an advantage over other modulation methods because CDMA techniques enable multiple base stations to simultaneously use the same channel space to communicate information. Thus, CDMA techniques permit channel overlap between base stations, which has a number of significant advantages in wireless communication systems, including the reduction of interference between mobile terminals and base stations, the exploitation of wireless network multipath components, and the simultaneous modulation and demodulation of information on multiple channels with multiple base stations.
Soft handoff is one method that uses these advantages to reduce error and increase the quality of service for wireless CDMA networks. Soft handoff is a steady-state condition wherein a mobile terminal simultaneously communicates identical information with a plurality of base stations. Soft handoff increases transmission and reception diversity at the mobile terminal, thereby increasing information capacity and quality of service while reducing the requisite signal to noise power ratio necessary to reliably communicate information. Soft handoff typically exists throughout a mobile terminal""s network connection; nonetheless, the plurality of base stations that communicate with the mobile terminal may change as the mobile terminal physically changes location, thereby requiring the mobile terminal to switch the base stations with which it communicates.
In order to implement soft handoff within a wireless CDMA network, a mobile terminal and the plurality of base stations it communicates with must perform certain functions in order to maintain the plurality of mobile terminal-base station network connections. First, the mobile terminal must receive multiple redundant base station transmissions on the forward link from the plurality of base stations to the mobile terminal and combine these redundant transmissions to aggregate the information sent by the plurality of base stations. This aggregation reduces the information error rate and increases the quality of service for the mobile terminal. The base stations must use identical CDMA symbols to modulate information and synchronize their redundant transmissions to the mobile terminal on the forward link for the mobile terminal to accurately aggregate and demodulate the redundant transmissions received from the base stations.
In addition, the plurality of base stations receive multiple redundant mobile terminal transmissions on the reverse link from the mobile terminal to the plurality of base stations. A mobile switching center aggregates or selects appropriate transmissions from the multiple redundant transmissions received by the base stations in order to reduce the error rate and maintain a sufficient quality of service. Thus, the mobile terminal must also synchronously transmit information modulated with identical CDMA symbols to the plurality of base stations for the mobile switching center to aggregate or select the redundant transmissions received from the mobile terminal by way of the different base stations.
Modern wireless IP architectures use IP-based protocols to communicate messages in data packets between mobile terminals and base stations and specifically IP version 4 (xe2x80x9cIPv4xe2x80x9d) protocols. In these architectures, IP base stations are connected to a wireless IP backbone network through edge routers, which interface the IP base stations with the IP backbone network. Each IP base station performs dual functions as both an RF front end for base station-mobile terminal communications and as a real-time router for IP data packets communicated between the mobile terminals and the wireless IP backbone network. The wireless IP backbone network further includes an IP-based control plane to route messages to and from the IP base stations that communicate with the mobile terminals.
Variations of wireless IP architectures include architectures wherein each base station""s coverage area defines an IP subnet. In these xe2x80x9call IPxe2x80x9d architectures, each base station has its own IP subnet address, and each base station and mobile terminal requires layer 3 mobility management techniques to communicate messages between the base station and a mobile terminal as the mobile terminal crosses a cell boundary. Thus, a mobile terminal may require an IP subnet address change when it crosses from one cell site to another using Mobile IP, DHCP, DRCP, or other layer 3 mobility management techniques.
Supporting soft handoff of mobile terminals in xe2x80x9call IPxe2x80x9d architectures is accomplished using IP multicasting to simultaneously communicate information between a mobile terminal and a plurality of base stations. IP multicasting is a method wherein a plurality of multicast group participants are part of a multicast group. Whenever a message is broadcast to the multicast group, the message is sent to every multicast group participant.
Soft handoff of a mobile terminal can be visualized as a layer 2 multicasting process, wherein identical information is transmitted to a mobile terminal from an IP network via a plurality of multicast participants that are members of the mobile terminal""s multicast group. Each multicast participant is an IP network interface that resides at the mobile terminal. When the plurality of multicast participants are established at the mobile terminal, a corresponding number of multicast network connections are created between the IP network and the mobile terminal. The IP network and the mobile terminal simultaneously communicate identical information via these separate multicast network connections by sending and responding to messages multicast to the mobile terminal""s multicast group. Thus, soft handoff of the mobile terminal is accomplished by establishing a multicast group corresponding to the mobile terminal, creating a plurality of multicast participants within the mobile terminal""s multicast group located at the mobile terminal, and communicating information between the mobile terminal and the IP network as multicast messages to the mobile terminal""s multicast group.
In the context of a wireless CDMA IP network, each multicast network connection corresponds to a communication channel between a mobile terminal and a base station. When a plurality of multicast participants are created at a mobile terminal, each multicast participant corresponds to a multicast network connection between a base station and the mobile terminal. Each multicast network connection originates at one of the base stations and ends at the mobile terminal as a multicast IP network interface. Thus, a plurality of wireless CDMA IP network connections exist between the mobile terminal and the IP network through the plurality of multicast network connections between the base stations and the mobile terminal.
Once the plurality of multicast participants and multicast IP interfaces are established at the mobile terminal, information is communicated between the mobile terminal and the base stations by broadcasting the information to the mobile terminal""s multicast group. The mobile terminal""s multicast group is identified by the IP multicast address assigned to the mobile terminal that associates the mobile terminal with its multicast group and group participants. Multicast messages between the base stations and the mobile terminal are modulated and demodulated using CDMA techniques, thereby allowing the mobile terminal and its multicast network connections to share channel space with other mobile terminals and their multicast network connections while maintaining a soft handoff condition with the wireless CDMA IP network.
When providing soft handoff of mobile terminals using IP multicasting, the IP network must allocate IP multicast addresses to the mobile terminals in order to facilitate IP multicasting with the mobile terminals. Currently IPv4 is the dominant Internet protocol used for Internet communications. IPv4 uses a 32 bit addressing scheme. A number of issues arise when determining how to allocate IP multicast addresses to mobile terminals. One issue that arises is how to utilize IP address servers in order to allocate and distribute IP multicast addresses. Traditional wireless IP networks use Dynamic Host Configuration Protocol (DHCP) servers to allocate unicast IP addresses to mobile terminals in wireless IP networks. Unicast IP addresses are ordinary IP addresses that are used by the IP network to establish non-multicasting network connections between the IP network and a mobile terminal. These servers do not have the capability to offer, assign and distribute IP multicast addresses to mobile terminals, and thus ordinary DHCP servers cannot allocate IP multicast addresses to mobile terminals.
Another issue that arises when determining how to allocate IP multicast addresses to mobile terminals is determining what types of IP multicast addresses to allocate, and how to allocate them, particularly within the limitations of IPv4. The Internet Assigned Number Authority (IANA) provides a total of 228 IP addresses for use as IP multicast addresses, of which 224 IP multicast addresses are provided for administratively scoped purposes. Administratively scoped IP multicast addresses are valid only within the domain of a particular administration, and thus identical administrative IP multicast addresses can be used simultaneously in different administrative domains without interference. In contrast, non-administratively scoped IP multicast addresses can only be used once regardless of the domain wherein the non-administrative IP multicast address is assigned and distributed.
These and other problems with the allocation of IP multicast addresses to mobile terminals when performing soft handoff of mobile terminals using IP multicasting are addressed by the present invention, which is a multicast address method for facilitating communication between nodes in xe2x80x9call IPxe2x80x9d architectures that support soft handoff via IP multicasting and CDMA techniques. The present invention allocates administrative IP multicast addresses to mobile terminals within different administrative domains to promote efficient use of IP multicast addresses and maps unique mobile terminal identifiers to IP multicast addresses, thereby enabling the wireless IP network to track IP multicast address allocations to mobile terminals. The present invention also includes a multicast DHCP server that offers, assigns and distributes IP multicast addresses when allocating IP multicast addresses to mobile terminals. The present invention further includes a mobile terminal soft handoff protocol for allocating IP multicast addresses to mobile terminals and establishing soft handoff of the mobile terminals via IP multicasting.
The present invention allocates IP multicast addresses to mobile terminals from the 224 (approximately 16.7 million) administratively scoped IP multicast addresses that can be allocated irrespective of other administrative domains. The same administrative IP multicast address can be simultaneously allocated to different mobile terminals that reside in different administrative domains because administrative IP multicast addresses are only valid within their particular administrative domain. If a plurality of mobile terminals that reside in different administrative domains are allocated an identical administrative IP multicast address, each administrative IP multicast address is valid only within the particular administrative domain wherein each mobile terminal resides. Thus, each of the plurality of mobile terminals may use an identical administrative IP multicast address without interfering with the other mobile terminals that reside in different administrative domains. Allocation of administrative IP multicast addresses to mobile terminals thereby promotes efficient use of the available IP multicast address space by enabling simultaneous allocation of identical IP multicast addresses to different mobile terminals within different administrative domains.
Each administrative domain includes a domain administrator that has the ability to allocate administrative IP multicast addresses to mobile terminals within its administrative domain. Whenever a domain administrator allocates an IP multicast address to a mobile terminal, the IP multicast address is an administrative IP multicast address from the administrative IP multicast address pool for that administrative domain. Thus, whenever a mobile terminal requests an IP multicast address from the IP network, the domain administrator serving the mobile terminal allocates an administrative IP multicast address from its administrative IP multicast address pool irrespective of other administrative domains. The mobile terminal receives the administrative IP multicast address from the domain administrator as its IP multicast address for its multicast address group.
The domain administrator allocates an IP multicast address to a mobile terminal by mapping a unique mobile terminal identifier from the mobile terminal to the administrative IP multicast address allocated to the mobile terminal. A mobile terminal identifier is any unique identification feature that distinguishes a mobile terminal from other mobile terminals and may include, e.g., the mobile terminal""s International Mobile Subscriber Identity (IMSI), Mobile Serial Number (MSN), or any other unique mobile terminal feature. By mapping a mobile terminal to its IP multicast address using a mobile terminal identifier, the wireless IP network is able to determine a mobile terminal""s IP multicast address and communicate information to the mobile terminal by broadcasting the information as a multicast message to the mobile terminal""s IP multicast address.
When a mobile terminal traverses from one administrative domain to another, it broadcasts a system ID in the other administrative domain, using standard physical layer CDMA pilot techniques. When this occurs, the new administrative domain goes through the standard procedures, and the mobile terminal releases its administrative IP multicast address from its former administrative domain and receives a new multicast address that is valid in its new administrative domain. However, where the administrative domains are operated by different communication companies, there may be agreements between the two companies allowing for a mobile terminal to retain both its new and its old multicast addresses in a limited area of overlap of the two administrative domains.
In order to allocate IP multicast addresses, the present invention includes multicast DHCP servers to allocate IP multicast addresses to mobile terminals. Multicast DHCP servers perform the unicast IP address allocation functions of traditional DHCP servers, but also include functions to offer, assign and distribute IP multicast addresses to mobile terminals. When a mobile terminal contacts a multicast DHCP server with a request for an IP multicast address, the multicast DHCP server responds to the IP multicast address request by offering, assigning and distributing an IP multicast address to the mobile terminal. The multicast DHCP server also records the mobile terminal identifier and IP multicast address of the mobile terminal to track the current use of IP multicast addresses, and for future use when allocating IP multicast addresses to the mobile terminal and other mobile terminals.
When allocating IP multicast addresses to a mobile terminal, the multicast DHCP server attempts to offer, assign and distribute an IP multicast address to the mobile terminal that has been allocated to the mobile terminal in a prior allocation by the multicast DHCP server. The multicast DHCP server allocates prior IP multicast addresses to the mobile terminal by mapping the mobile terminal""s unique mobile terminal identifier to IP multicast addresses that the multicast DHCP server has allocated to the mobile terminal in previous IP multicast address allocations. The multicast server uses both the IP multicast address and the mobile terminal ID to check for possible IP multicast addresses that the multicast DHCP server has allocated to the mobile terminal previously. Where the administrative domain is a very large geographic area, the process may be more efficiently handled by using multiple DHCP servers within a single domain.
As noted above, by cross referencing on a multicast or a mobile terminal ID, a multicast server can allow a mobile terminal to add a new multicast address while retaining its old multicast address, using data base management techniques.
By allocating a prior IP multicast address to a mobile terminal, the IP network reduces data caching at the mobile terminal and increases the probability that the IP network can locate the mobile terminal using its IP multicast address.
When a mobile terminal has received an IP multicast address from a multicast DHCP server, the mobile terminal simultaneously communicates with a plurality of IP network nodes once a plurality of multicast network connections have been established and soft handoff has occurred. Within xe2x80x9call IPxe2x80x9d wireless network architectures, each base station includes its own IP subnet address and acts as a separate IP network node. Thus, when a mobile terminal simultaneously communicates with a plurality of IP base stations via IP multicasting in xe2x80x9call IPxe2x80x9d wireless network architectures, the mobile terminal simultaneously communicates with a plurality of IP network nodes while in soft handoff.
In order to establish soft handoff with a plurality of IP network nodes, the mobile terminal must establish a plurality of multicast network connections between itself and the IP base stations. These multicast network connections are established by means that include a mobile terminal multicasting soft handoff process wherein a mobile terminal acquires an IP multicast address and enters into soft handoff with the IP network.
Upon power up and registration with the IP network, the mobile terminal initially secures a plurality of unicast IP addresses from the IP network nodes. Each node allocates one unicast IP address to the mobile terminal which is associated with a particular network interface, and thus the number of unicast IP addresses secured by the mobile terminal corresponds to the number of IP network nodes that the mobile terminal will communicate with during soft handoff. For a wireless CDMA IP network, each unicast IP address corresponds to a network interface on that terminal and to a base station""s CDMA pilot signal.
The mobile terminal then acquires an IP multicast address from a multicast DHCP server within the mobile terminal""s administrative domain. The multicast DHCP server records the allocation of the IP multicast address to the mobile terminal using its unique mobile terminal identifier, thereby avoiding allocation of duplicate IP multicast addresses to different mobile terminals within the mobile terminal""s administrative domain. The mobile terminal registers its unicast IP addresses with a multicast agent by transmitting its unicast IP addresses, mobile terminal identifier and IP multicast address to the multicast agent, thereby creating a plurality of multicast network connections. The multicast agent generates a table of unicast IP addresses and their corresponding mobile terminal identifier and IP multicast address, and forwards this unicast IP address table to the IP network edge routers. The IP network edge routers are configured to substitute a mobile terminal""s IP multicast address for any corresponding unicast address when communicating information between the wireless IP network and the mobile terminal. Thus, when information is communicated using a mobile terminal""s unicast IP address, the edge routers replace the unicast IP address with the mobile terminal""s IP multicast address, thereby multicasting the original unicast information to the mobile terminal. When the mobile terminal ends its IP network connection, it notifies the multicast DHCP server and releases its IP Multicast address, thereby releasing its IP multicast address and enabling the multicast DHCP server to allocate the IP multicast address previously allocated to the mobile terminal to another mobile terminal in response to an IP multicast address request.
Thus, in accordance with an aspect of our invention, a multicast agent registers IP network connections for the mobile terminals as multicast connections. Further, in addition to the DHCP server already employed, a second multicast DHCP server within an administrative domain allocates multicast addresses to the mobile terminals.